Remeha Avanta boiler - pressure quickly goes from very low to very high

[mjgreen81]

Hi everyone,

I had my bathroom suite replaced over the summer, including a new bath, shower, pump etc etc.

Since the work had been completed I had noticed that the pressure in my Remeha Aventa condensing boiler seems to go from very low (less than 0.5 bar) to very high (~2.5 bar) quite quickly. If I top up the system (when it is cold) to 1 - 1.5 bar (as it should be), when the water is heated the pressure will get too high and it will release some. It then returns to around 0.5 bar (when cold) and the cycle would continue.

This wasn't really causing me a problem until I went to switch on the central heating for the first time this weekend. After a short time I could hear the boiler clunking away as the pressure was too low. I topped it up but after a short time it would start clunking away again.

Presumably having the system heating the hot water and the central heating is causing too much pressure in the system and the PRV is dumping it outside.

I have not opened up the boiler to have a look yet, but would I be correct in suspecting that the likely cause of this kind of issue would be that the expansion vessel requires recharging? In my mind if the expansion vessel has no air pressure than the vessel is effectively already full of water with nothing for it to expand into. Is that the correct theory?

I plan to find some time over the next couple of days but would like to prepare myself with the likely issues before I have a look so I can check all the obvious things. Last year some gunk went through the boiler which broke the PRV, pressure gauge (both of which I had to replace) and I also recharged the expansion vessel so I am happy to take on the basics with this boiler.

Thanks in advance for your help.

Mike

 

[flameport]

but would I be correct in suspecting that the likely cause of this kind of issue would be that the expansion vessel requires recharging? In my mind if the expansion vessel has no air pressure than the vessel is effectively already full of water with nothing for it to expand into. Is that the correct theory?

That is correct.

After locating the valve on the expansion vessel, press the centre in - if air escapes, it has at least some charge. If nothing, then it needs to be recharged. If water comes out, it has failed internally and must be replaced.

 

[dreadnoughtheating]

Ahh, but behind the front cover (which makes it 'room-sealed') is Gas Installer territory, so the DIYNot forum rules oughta some into play here.... surely

DH

 

[mjgreen81]

Thanks Flameport, will give it a check.

Dreadnoughtheating - there are loads of discussion/threads etc about recharging the expansion vessel on DIYNot.

 

[dreadnoughtheating]

Indeed there are, but in the
Avanta it is inside the casing, which forms the room sealed compartment.
Hence it is not a 'diy' area.
I trust that when you have refitted it you have made all the checks necessary to ensure it's integrity?
Beleive it or not, and only you know the real answer to that one, this is for everybodies protection, yours, your families and any visitors.
DH

 

[mjgreen81]

Just to confirm that the expansion vessel was completely empty of air as suspected.

I drained the boiler last night, refilled the expansion vessel to 1bar (as per the instruction manual) and refilled the boiler via the filling loop. The system performed much better (radiators were getting nice and hot etc) but after an hour or so the boiler would start clunking away again. After turning the CH and HW off again and allowing the system to cool, the pressure had dropped again.

I allowed everything to cool before going to bed last night, used the filling loop to re-pressure the system to 1bar and left it overnight. When I checked this morning he pressure had dropped again.

I suspect the PRV is knackered again following the fact that water has been escaping via it. The escape pipe outside was dripping this morning but it was hard to tell how much had escaped due to the rain. I have taped a plastic bag over the pipe and re-pressurised the system just to make double sure that is where I am losing the pressure.

....I will check again in a bit

 

[hertsboilers]

As DH said, not only combustion chamber, but PRV is also a safety device for boilers. You shouldn't have played with it really!